Plant growth regulators (PGRs) affect growth and differentiation of plants. More specifically, various PGRs can, for example, reduce plant height, stimulate seed germination, induce flowering, darken leaf coloring, minimize lodging of cereals, change the rate of plant growth, and modify the timing and efficiency of fruiting.
PGRs are recognized as an essential tool in modern cotton production. Mepiquat (IUPAC name: N,N-dimethylpiperidinium), the first widely accepted PGR for cotton plants, is typically applied to cotton plants in the form of its chloride salt, i.e., mepiquat chloride (the chlorine salt of mepiquat), by foliar application.
The most visible effect of mepiquat chloride PGRs on cotton plants is the reduction of overall plant height, reduction of the distance between nodes, and reduction of plant width. In turn, light penetration to the lower leaves of the plant is enhanced, promoting lower boll retention and development.
A related benefit that is often achieved is an increase in the weight of harvestable cotton bolls. Another highly desirable benefit that is often achieved by using mepiquat chloride PGRs is "earliness" of boll opening. See, for example, Khafaga, Angew. Botanik 57, 257-265 (1983); Sawan et al., J. Agronomy & Plant Science, 154, 120-128 (1985); Ray, Deciphering PGRs, Cotton Farming, June 1997, 18-20; Cotton Production, 1995 Delta Agricultural Digest, 22-24, (published by Argus Agronomics, a division of Argus, Inc.); U.S. Pat. No. 3,905,798, U.S. Pat. No. 4,447,255; Pix Official Handbook.
As discussed in U.S. Pat. No. 3,905,798 to Zeeh et al., all of the known mepiquat salts are hygroscopic solids. Accordingly, dry flowable forms of mepiquat plant growth regulators must be prepared by using various solid carriers such as clays, fertilizers, or the like, or by employing special preparation procedures and packaging that isolate the solids from any humidity in the environment. Further, 95/02963 teaches a process for processing and drying hygroscopic mepiquat chloride for solids formulations and in particular for the production of tablets.
Furthermore, EP-A 573 177 for example discloses an anhydrous process for manufacturing mepiquat chloride, wherein the resulting product must be packed in a water-soluble polyvinylalcohol pouch to protect it against moisture and dissolution as a result of water vapor being taken up.
94/09627 describes the production of water-dispersible granules of mepiquat chloride. Ways are shown of overcoming the hydrgroscopic problems with the aid of selected auxiliaries, e.g., synthetic calcium silicates, binders and mixtures of various sodium sulfonates and/or carboxylates.
In the manufacturing environment, the hygroscopic nature of the mepiquat salts is undesirable for various reasons. In particular, moisture causes the mepiquat chloride salt compositions to disassociate into ions, which in turn tend to have a relatively low pH. The net result is a relatively strong corrosive effect when the moist solids are stored for any substantial period of time. Furthermore higher concentrations of chloride anions in water show strong corrosive effects towards many steel types and metalls. Accordingly, special manufacturing processes and apparatuses are typically employed in order to overcome the corrosive nature of the mepiquat salts.
Further, monoborates of mepiquat, especially monoborates, monoborate chelates or complexes, are used as toners for electrophotography (cf, e.g., JP-A 05/265257; JP-A 02/166713). Aliphatic, open chain quatery ammonium monoborates are described in Electrochim. Acta 39, 18 (1994); Z. Naturforsch. B (Chim. Sci.) 48, 7 (1993); Z. Naturforsch. B (Anorg. Chem. Org. Chem.) 33 B, 20 (1978); J. Nonmetals 2 (2), 103 (1974); JP-A 89/322006; U.S. Pat. No. 3,403,304). These known ammonium monoborates are used as electrolytes, catalytic polymerisation agents, flame retardants or boron-biocides. However no applications are described of these compounds in the agricultural sector.
Although the hygroscopic and corrosive nature of the mepiquat chloride salts is a known problem, no alternative mepiquat compounds have been proposed that are not hygroscopic or corrosive. The search for such compounds is complicated by the requirement that modifications to the compound to decrease its corrosive and hygroscopic properties, must not substantially harm the plant growth regulating properties of the compound. Otherwise, the utility of mepiquat would be eliminated or substantially impaired.
In view of such biological activity considerations and further in view of the uniformly hygroscopic nature of all known mepiquat salts, no modified mepiquat compounds which minimize or eliminate these problems while still retaining high biological activity have been proposed.